The invention relates to a brake device for a two-wheeled vehicle and, in particular, to a method for controlling a braking force and a device for controlling the braking force in a combined brake system in which front and rear brake devices are operated in an interlocking manner.
As a brake device for a two-wheeled vehicle, a brake device called a combined brake system has conventionally been available. In this combined brake system, when one of front and rear brake devices is operated, a braking force is also generated in the other brake device in an interlocking manner. This combined brake system is available in a mechanical type (CBS) and an electronically controlled type (eCBS). In the combined brake system of the mechanical type, the front and rear brake devices are connected by a hydraulic circuit and a mechanical element. A pressure of brake fluid is set such that the braking force is distributed to the front and rear brake devices at a specified ratio (for example, front 6:rear 4) when a braking operation is performed on the combined brake system of the mechanical type.
Meanwhile, in a case of the combined brake system of the electronically controlled type, the front and rear brake devices are not connected by the hydraulic circuit or the mechanical element. The front and rear brake devices are operated in the interlocking manner by electronic control. Accordingly, braking-force distribution to the front and rear brake devices can flexibly be changed in accordance with a switching operation by a rider or a speed of the two-wheeled vehicle.
As an example of the combined brake system of the mechanical type, one as will be described below exists (see). This is a brake device capable of increasing the braking-force distribution to a rear wheel during an operation of a brake pedal. More specifically, a first master cylinder that is actuated by a brake lever is connected to a brake caliper of a front wheel, a mechanical servomechanism that generates a brake hydraulic pressure by actuation of the brake caliper is connected to a brake caliper of the rear wheel via a pressure control valve that decreases a braking force on the rear wheel in a manner to follow a braking-force distribution characteristic of the front and rear wheels. In addition, a brake hydraulic pressure from a second master cylinder that is actuated by the brake pedal is transmitted to the brake caliper of the rear wheel via the mechanical servomechanism and the pressure control valve and, at the same time, increases a maximum braking force on the rear wheel by changing a pressure decreasing characteristic of the pressure control valve.